Math Is Fun Forum

acanter84

Member

Registered: 2012-06-12

Posts: 1

Need help with problem PLEASE!!!

Last month sharons deli charged the business club $231 for 18 chicken lunches and 14 ham lunches. This month the charge was $225.00 for 15 chicken lunches and 16 ham lunches. The bill does not list the price of a single chicken or ham lunch but you need to know this
So you can bill the members individually. How much did a single chicken lunch cost?

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Need help with problem PLEASE!!!

Hi acanter84;

Ham is $7.50 and chicken is $7.00. Welcome to the forum.

---

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

bola

Member

Registered: 2012-06-13

Posts: 8

Re: Need help with problem PLEASE!!!

i have these assignment to submit will want to kmow if my answers are right.
1.if the time a student stays in a classroom follows the normal distribution with meu=6hr, s.d=0.1hr,what is the probability that he stays in a classroom for less than 5hours.
2.A factory produces a tv sets by process A or by process B.Assuming that the life time distribution of the sets is normal.The sets produced by process A have mean lifetime of 86,000hr with s.d 8,000hr,whereas those produced by process Bhave mean lifetime of 75,000hr with s.d 6,000hr sets with a life time of less than 30,000 hr are regarded as definitely bad.which of the two processes will produce more acceptable sets
3.A factory produces apple juice cointained in a bottle of 1.5 litres.However due to random fluctuation in the automatic bottling machine,the actual vol.per bottle varies according to anormal distribution.It is observed that 10% bottle are under 1.45 litres whereas 5% contain more than 1.55litres.calculate the mean and s.d of the volume distribution.My ans.1=-10,2=A=-7,B=-7,5,3.i dinot attempt it Thanks.

Bob

Administrator

Registered: 2010-06-20

Posts: 10,582

Re: Need help with problem PLEASE!!!

hi bola,

Welcome to the forum!

Your question nearly got lost, because you attached it someone else's post.  Suggest you always start a new post.

However did you get -10 for Q1 ?

The question asks for a probability so your answer should be in the range 0 --> 1

Let's get that one sorted and then we can move on to the others.

Bob

---

Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob

bola

Member

Registered: 2012-06-13

Posts: 8

Re: Need help with problem PLEASE!!!

hi bola,

Welcome to the forum!

Your question nearly got lost, because you attached it someone else's post.  Suggest you always start a new post.

However did you get -10 for Q1 ?

The question asks for a probability so your answer should be in the range 0 --> 1

Let's get that one sorted and then we can move on to the others.

Bob

thanks very much for this quick respose bob.

1.if the time a student stays in a classroom follows the normal distribution with meu=6hr, s.d=0.1hr,what is the probability that he stays in a classroom for less than 5hours.
Now let get the first question sorted as u suggested.Im not that good in probability.

i used the formula    z=x-meu
                                  ------
                                  s.d

and this bring me to   Z= 5-6
                                      ----   =-10
                                      0.1
and since there is no -10 in the table i stopped here.

Last edited by bola (2012-06-15 23:25:23)

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Need help with problem PLEASE!!!

Hi bola;

You did not answer Bob's question. -10 is the number of standard deviations from the mean that 5 hours is but it is not the probability. That is always a number between 0 and 1 inclusive.

A small question. Less than -10 sd's is going to be a very small probablity. You can calculate it but not using a table. So I am wondering if you copied the question correctly?

---

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

bola

Member

Registered: 2012-06-13

Posts: 8

Re: Need help with problem PLEASE!!!

the question states that
what is the probability that the student stays in classroom for less than 5hr  if meu(u) =6hr and s.d =0.1hr

bola

Member

Registered: 2012-06-13

Posts: 8

Re: Need help with problem PLEASE!!!

i used the formula    z=x-meu
                                  ------
                                  s.d

and this bring me to   Z= 5-6
                                      ----   =-10
                                      0.1
and since there is no -10 in the table i stopped here.

Last edited by bola (2012-06-15 23:07:59)

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Need help with problem PLEASE!!!

Hi;

Yes, the answer is too small for a chart. It is

This is too small for any chart I know.

---

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

bola

Member

Registered: 2012-06-13

Posts: 8

Re: Need help with problem PLEASE!!!

how do i go about it then

bola

Member

Registered: 2012-06-13

Posts: 8

Re: Need help with problem PLEASE!!!

Thanks the second question is this and i got -7 for process A and -7.5 for process B

2.A factory produces a tv sets by process A or by process B.Assuming that the life time distribution of the sets is normal.The sets produced by process A have mean lifetime of 86,000hr with s.d 8,000hr,whereas those produced by process Bhave mean lifetime of 75,000hr with s.d 6,000hr sets with a life time of less than 30,000 hr are regarded as definitely bad.which of the two processes will produce more acceptable sets

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Need help with problem PLEASE!!!

Hi;

You need to integrate this either symbolically or numerically.

Symbolically you will get

This is most easily done by taking it over to Wolfram.

---

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

Bob

Administrator

Registered: 2010-06-20

Posts: 10,582

Re: Need help with problem PLEASE!!!

hi bola,

I agree with bobbym on Q1.  Those figures don't go well together, so check the numbers.  The method is OK.

Now for Q2.

I've put a rough sketch of the two normal distributions together.  The red line is at 30,000 hr.

I think you are meant to calculate the area to the left of that line for each distribution and so decide which type A or B is less likely to produce a bad set.

Bob

---

Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob

bola

Member

Registered: 2012-06-13

Posts: 8

Re: Need help with problem PLEASE!!!

This is the third question

.A factory produces apple juice cointained in a bottle of 1.5 litres.However due to random fluctuation in the automatic bottling machine,the actual vol.per bottle varies according to anormal distribution.It is observed that 10% bottle are under 1.45 litres whereas 5% contain more than 1.55 litres.calculate the mean and s.d of the volume distribution.My ans.

Bob

Administrator

Registered: 2010-06-20

Posts: 10,582

Re: Need help with problem PLEASE!!!

hi bola,

Am I correct in thinking you are OK now with Q1 and Q2 ?

Q3.  Call the mean mu and the standard deviation sigma.

Now exactly how you do the next bit will depend on the layout of your Normal distribution table.

I'll use this

http://www.mathsisfun.com/data/standard … table.html

so

and

So working the table 'backwards' (I have interpolated the 3rd decimal place)

and

So you have a pair of simultaneous equations and can solve for mu and sigma.

Hope that helps.

Bob

---

Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Need help with problem PLEASE!!!

Hi;

Nice solution Bob!

Hi bola;

This is most easily done by taking it over to Wolfram.

This is not exactly accurate. In the days before Wolfram there was a guy named Hastings. He was the best that ever lived at curve fitting. Know one knows how he did it. He may have come up with this:

This gets an excellent approximation for the area under the standard normal curve. With it we get:

which is very close to the actual answer.

---

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

Bob

Administrator

Registered: 2010-06-20

Posts: 10,582

Re: Need help with problem PLEASE!!!

hi bobbym,

i have these assignment to submit will want to kmow if my answers are right.
1.if the time a student stays in a classroom follows the normal distribution with meu=6hr, s.d=0.1hr,what is the probability that he stays in a classroom for less than 5hours.

It's an assignment.  Teachers don't set normal distribution questions where the the value is off the scale like this.  We have three numbers so I think the most likely explanation is the s.d. is 1 not 0.1

That brings the question back into the realms of normality (no pun intended).  It is Q1 out of 3 after all.

So I'm going for

Bob

---

Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Need help with problem PLEASE!!!

Hi Bob;

Yes, I agree. The probability that the question is asking for a sd of .1 is

---

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.